Fixed marine platform with dispersed base

ABSTRACT

A fixedly positioned marine platform held at the ocean floor by piles and the like, having a relatively flat concrete apron disposed about the platform lower end and also supported on the ocean floor. The apron functions to stabilize the platform against lateral forces caused by water and wave motion, and also avoids scouring which would otherwise occur about the platform legs and piles due to movement of water along the ocean floor. The apron further lowers the center of gravity of the structure and improves its resistance to vibrations and resonance effects due to wave motion.

United States Patent Pogonowski et al.

[ Sept. 23, 1975 FIXED MARINE PLATFORM WITH DISPERSED BASE [75] Inventors: lvo C. Pogonowski, Blacksburg, Va.;

Paul D. Carmichael, Houston, Tex.

[73] Assignee: Texaco Inc., New York, NY.

[22] Filed: Aug. 23, 1973 21 Appl. No.: 390,805

[52] US. Cl 61/46; 61/50 [51] Int. Cl. E02D 3/12; E02D 27/02 [58] Field of Search 61/46, 465, 50, 1

[56] References Cited UNITED STATES PATENTS 1,421,857 7/1922 Store 61/46 2,589,153 3/1952 Smith 61/46.5

2,940,265 6/1960 Doody et al. 61/46 3,117,423 1/1964 Fagerlund 61/46 3,518,835 7/1970 Perry 61/46 3,654,886 4/1972 Silverman 61/46.5

Primary Examiner-Jacob Shapiro Attorney, Agent, or Firm-T. H. Whaley; C. G. Ries; Robert B. Burns [57] ABSTRACT A fixedly positioned marine platform held at the ocean floor by piles and the like, having a relatively flat concrete apron disposed about the platform lower end and also supported on the ocean floor. The apron functions to stabilize the platform against lateral forces caused by water and wave motion, and also avoids scouring which would otherwise occur about the platform legs and piles due to movement of water along the ocean floor. The apron further lowers the center of gravity of the structure and improves its resistance to vibrations and resonance effects due to wave motion.

6 Claims, 5 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of 2 3,906,734

US Patent Sept. 23,1975 Sheet 2 of2 3,906,734

FIG. 4

FIG. 5

AWAY/Aw FIXED'MARINE PLATFORM WITH DISPERSED BASE BACKGROUND OF THE INVENTION In the use of offshore marine platforms which are fixedly positioned to the sea floor by pilings and the like, the problem of moving water and ocean currents can be troublesome in several ways. For one thing, constantly changing sea conditions can affect excessive periodic waves and water currents which could in turn set up harmful harmonics in the platform movement.

Further, in deeper offshore waters it is usually necessary to provide considerableweight at the platform lower end. This is to stabilize it more firmly against the above noted wind and wave conditions as well as to provide balance to the greater amount of steel necessitated in such deep water structures.

In the instance of any offshore platform however, a primary problem is the one caused by movement of water about the platform anchored or lower end. In virtually any location there will be a certain amount of water flow due to prevailing currents, to tide variations, and to other natural phenomena. In the instance of the firmly positioned or piled platform this water movement can be particularly harmful where the water tends to scour away the soil beneath the platform. Such action will tendto expose a greater length of the pile as well as a portion of the anchoring legs.

The stated problem has been particularly accentuated in the instance of platforms where the bottom structure is supplemented by tanks, storage facilities, templates or other sub-structures which would, by their presence, tend to alter the normal course of the flowing water. For example, where a storage facility has been incorporated into the platform lower end, water diverted through the platform legs has been found to scour a sufficient quantity of theocean floor away from the anchoring piles .and legs to jeopardize the stability of the structure.

In the arrangement of the marine'structure'presently contemplated, the lower end of the platform adjacent the ocean floor is provided with a relatively heavy apron or substantially horizontal skirt. A primary function of this apron, as it will be hereinafter referred to, is to engage the lower end of the platform to provide an additional weight factor thereby stabilizing the overall structure.

Since the apron is disposed adjacent to and about the respective legs of the platform, it in effect prohibits the scouring effect of ocean currents which would otherwise tend to erode away the sand and substrate and form shallow pits about the leg and anchoring piles.

The apron is formed preferably by pouring or depositing fluidized concrete or cement from a source above the waters surface, to the ocean floor. The concrete is initially retained within a flexible walled container which defines a partial enclosure about the fluidized material. The character of the flexible retainer is such that it will permit the fluidized material to normally flow about the platform legs, and yet maintain a desired depth. Thereafter, as the concrete hardens it will form a rigid yet widespread base or foundation. The flexible retainer can then be removed if feasible, or merely be permitted to wear away in the course of time such that only the concrete apron remains.

DESCRIPTION OF THE DRAWINGS FIG. .1 is a perspective view of a marine platform, as contemplated, shown fastened to the floor of a body of water. FIG. 2 is an enlarged segmentary view of the lower portion of the structure shown in FIG. 1. FIG. 3 is a sectional view taken along line 33 of FIG. 2. FIG. 4 is similar to FIG. 3, showing the flexible container in expanded condition, and FIG. 5 is similar to FIG. 4 showing a reinforcing member in the apron section.

Referring to FIG. 1, a characteristic marine structure 10 of the type proposed, includes a plurality of substantially vertically disposed support legs or columns 11, 12 and 13. These legs are shown as canted slightly inward at the top toward the structures central axis. The canting, however, is normally for the purpose of providing a greater area of distribution at the lower end of the platform, thus contributing to its stability.

In the normal manner, the respective upstanding support legs or columns are provided with sufficient cross bracing 14 and 16 to assure the physical and structural integrity of the unit. For higher platforms and deeper water the amount of structural reinforcing or stabilizing will be understandably greater.

A working deck 17 is normally positioned at the platform upper end, beyond the reach of water and waves. In the instance of a producing facility, deck 17 can contain pumping, separating, and other such equipment for handling crude materials as crude oil or gas. In the instance of a producing platform, deck 17 will be provided with the usual derrick, draw works, crew quarters, and the like to accomplish the desired drilling functions.

In either instance, the lower end of the respective elongated support legs 11, 12 and 13 are normally partially embedded into the substrate to support the weight of the platform itself. It is understandable that for a relatively soft substrate as in the instance of a deltaic location, the platform will tend to sink, rather deeply before coming to rest. For a more substantial or consolidated substrate, the platform will tend to rest on the surface of the ocean floor rather than embed itself.

In either instance the firm positioning of the platform is assured by inserting anchoring piles 18 to a predetermined point in the substrate where the stability of the platform is assured. These anchoring piles are normally guidably driven through the respective support legs. Each leg is consequently sufficiently large to accommodate a number of the piles. The depth to which the piles are forced is governed by several factors including the condition of the substrate, the expected weight to be carried by the platform, and the expected forces which will be exerted against it.

Under normal operating circumstances in the instance of a drilling platform a number of wells 19 will be drilled from the waters surface, down through the center of the platform and into the substrate. Thus, the interior defined by the lower end of the respective support legs, will be provided with a plurality of well heads 21.

In the instance of a storage or processing facility, platform 10 can be provided with a series of flow lines which are brought along the ocean floor and diverted upwardly through the center of the platform, or along the respective legs, to the deck.

In either instance the lower end of platform 10 is provided with a substantially flat apron or spread foundation footing 22 which is connected to and extends outwardly from the platform. In its preferred form, apron 22 comprises a relatively heavy slab or footing which, by virtue of its weight, will be partially embedded into the substrate about the platform to provide a firm foundation and anchor for the latter.

The preferred material of which apron 22 is formed is cement or concrete such that the latter can be initially injected in fluid form and subsequently hardened into a desired shape. This is achieved by introducing the fluidized, hardenable material into flexible walled, collapsible containers 23 carried at the platform lower end.

Said containers 23, as shown in FIG. 3 can be initially folded or otherwise compacted into a relatively small unit depending from platform members, prior to the platform being submerged to its subsea position. In such an instance the flexible walled containers 23 are attached to structural members of the platform at the latters lower end such as cross brace 14. The said flexible walled containers 23 are so designed to permit the heavy, fluidized material to flow in a desired pattern across the sea floor at the platform lower end. Preferably apron 22 will be formed to substantially surround the support legs and the respective piles 18, which would ordinarily be subjected to the greatest amount of erosion due to water flowing thereabout.

Thus, flexible walled containers 23 are positioned to surround, or at least partially enclose the respective support legs in a manner to direct fluid cement about the legs that would ordinarily be subject to the most severe erosion conditions. As shown in FIGS. 3 and 4 flexible walled member 23 includes a prefabricated bag-like member that is communicated with a source of the fluidized concrete through conduit 24. The latter extends along and is fastened to one or more platform legs 12 to the waters surface, preferably terminating at deck 17 such that fluid concrete can be deposited in the upper end thereof.

The shape or configuration of flexible member 23 is such that as fluidized concrete is introduced thereto it will tend to spread along the lower side of the said member as the heavy concrete assumes its normal horizontal disposition. Thus, the member 23 will be forced open by the weight of the concrete and expand to its fully unfolded position thereby defining at least a partial enclosure for the fluidized material.

A predetermined amount of the latter will thereafter be further introduced to provide the necessary thickness and additional weight required in the platform lower end as well as to provide the desired thickness to the poured apron 22.

Container 23 functions to form a resilient walled partial enclosure which can be subsequently removed or eroded away due to wear, water movement, abrasion and the like. Said member 23 can therefore be formed of a reinforced, basically flexible material such as rubber reinforced canvas or the like. Also reinforced neoprene or other suitable plastic material which can be prefolded and yet be spread by inflowing concrete.

Referring to FIG. 3, container 23 is, as shown, folded into a relatively tight compact body 26. As platform 10 is being transported along the waters surface, said body or pack 26 can futther be further within a rigid, temporary closure to prohibit its being prematurely opened as a result of contact with wind or water as the platform is moved.

However, as platform 10 is permitted to controllably submerge to its resting place at the ocean floor, the restraints or other protective members are released from folded pack 26. Thus, the latter will be free to unfold and/or adjust, in response to water movement about the platform lower end. Preferably, pack 26 will maintain its shape until the platform is settled on the ocean floor to avoid the flexible members 23 becoming entangled in the platform legs.

Thereafter, with platform 10 positioned as desired, and piled into place, fluidized cement is introduced through conduit 24, the lower end of which terminates within the partial enclosure of said member 23. The continuous flow of the concrete or cement into the enclosure will displace water to completely open the latter, regardless of its initial disposition. Thus, the predetermined amount of concrete will flow outwardly away from the platform base. Eventually, flexible walled member 23 will be stretched to its maximum expanded position thereby permitting the concrete to build up to its desired thickness rather than merely to spread about the floor. The enclosure is thus designed in such manner when in open position to accommodate the set amount of the concrete which will eventually form the desired apron 22.

As shown in FIGS. 4 and 5, a portion of the enclosure within flexible member 23 can be arranged to fall within the periphery of the respective support legs. Thus, the concrete will reach into said area as well as external to the periphery of the base.

Toward facilitating the disposition of the apron 22 an upstanding plate 27 or similar cross member formed of spaced apart bars is disposed about the platform lower end forming a retaining wall for concrete thereby delivering it as required to the inner or the outer base sections.

Since in the instance of most concrete or cement structures a degree of reinforcing is often required, the latter can be provided in the form of a steel mesh wire 28 or the like. Further, said material as shown in FIG. 5 can be initially rolled into such form as to open concurrently with the opening or expansion of the flexible walled member 23 which will enclose not only the subsequently poured cement, but also the reinforcing element. Flexible walled member 23 will thus serve as a retainer for the reinforcing element until such time as both members are released from the platform at its subsea position.

Other modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. .A marine structure having substantially vertical rigid support leg means, the lower ends of the latter being adapted for embedment into the floor of a body of water to anchor the structure in said body of water,

an apron disposed adjacent to and surrounding said support leg means when the latter is embedded, being firmly connected to said vertical support leg means to form a unitary part of said platform, said apron extending outwardly from the leg means and resting on the floor of said body of water,

said apron being formed of a hardenable, fluidized material which has hardened to provide a rigid sur face thereon after being deposited in fluid condition onto said floor about said support leg means.

2. In an apparatus as defined in claim 1, wherein said apron includes a plurality of apron segments fastened to and extending outwardly from said support leg means in a direction away from said marine structure.

3. In an apparatus as defined in claim 1, wherein said apron includes a plurality of apron segments, each segment thereof being connected to and disposed between spaced apart legs of said support leg means.

4. In an apparatus as defined in claim 1, wherein said apron includes a plurality of apron segments being mutually interconnected to form a substantially continumeans. 

1. A marine structure having substantially vertical rigid support leg means, the lower ends of the latter being adapted for embedment into the floor of a body of water to anchor the structure in said body of water, an apron disposed adjacent to and surrounding said support leg means when the latter is embedded, being firmly connected to said vertical support leg means to form a unitary part of said platform, said apron extending outwardly from the leg means and resting on the floor of said body of water, said apron being formed of a hardenable, fluidized material which has hardened to provide a rigid surface thereon after being deposited in fluid condition onto said floor about said support leg means.
 2. In an apparatus as defined in claim 1, wherein said apron includes a plurality of apron segments fastened to and extending outwardly from said support leg means in a direction away from said marine structure.
 3. In an apparatus as defined in claim 1, wherein said apron includes a plurality of apron segments, each segment thereof being connected to and disposed between spaced apart legs of said support leg means.
 4. In an apparatus as defined in claim 1, wherein said apron includes a plurality of apron segments being mutually interconnected to form a substantially continuous hard surface on the ocean floor, about the periphery of said marine structure.
 5. In an apparatus as defined in claim 1, wherein said apron is formed of concrete.
 6. In an apparatus as defined in claim 3, wherein said marine structure includes a plurality of support legs, and leg reinforcing means extending intermediate adjacently positioned support legs, said apron segments being formed about and embedding said reinforcing means. 